1. Field of the Invention
The invention relates to the production of nitrogen from air. More particularly, it relates to the production of dry, high purity nitrogen.
2. Description of the Prior Art
Permeable membrane processes and systems have been proposed and used increasingly for the production of nitrogen by air separation. In such operations, feed air is brought into contact with the surface of the membrane, and oxygen, as the more readily permeable component of air, passes through the membrane while nitrogen, the less readily permeable component of air, is withdrawn from the membrane system as a non-permeate product stream. Conventional membrane systems typically produce nitrogen having purity levels of up to about 99.5%. For some applications, however, a high purity nitrogen product, i.e. nitrogen having a purity of about 99.95% or more, e.g. 99.9995% purity, is required.
The conventional method of achieving such high nitrogen purity levels is to pass the product nitrogen from a membrane system to a deoxygenation system, i.e. a deoxo system, which is capable of converting residual oxygen in the product nitrogen stream to water by combining said oxygen with hydrogen in the presence of a noble metal catalyst. The resulting high purity nitrogen product generally will contain less than 5 parts per million by volume (ppmv) oxygen. However, it will also contain substantial quantities of water, e.g. from about 10,000 to about 40,000 ppm, as well as some excess hydrogen from the deoxo system. In many practical applications, it is desirable to remove such moisture from the high purity nitrogen stream, either to prevent condensation thereof and subsequent corrosion or freezing in the piping and instrumentation of downstream applications of said high purity nitrogen, or because the presence of such moisture is incompatible with the desired end use of the high purity product nitrogen stream recovered from the membrane/deoxo systems.
For purposes of removing moisture from the high purity nitrogen stream, aftercooler, moisture separator and adsorptive (or refrigerated) dryer units are generally incorporated into the overall system. While these units are effective in removing moisture so as to produce an essentially dry, high purity nitrogen product, they significantly increase the complexity of the overall process, reduce reliability, and may also result in a significant loss of nitrogen product. Such undesired loss of product is the result of purge requirements, blowdown losses and the like. In addition, this conventional approach for moisture removal may require the expenditure of a significant amount of additional energy for regeneration or refrigeration purposes.
It can be appreciated, therefore, that a desire exists in the art for improved processes and systems for the production of dry, high purity nitrogen product. In particular, this desire relates to improvements pertaining to the removal of moisture from high purity nitrogen produced by the convenient use of membrane/deoxo systems for air separation. More particularly, it is desired that effective removal of moisture be achieved at relatively low cost and energy consumption, without the significant product loss associated with the conventional use of adsorptive (or refrigerated) dryer units.
It is an object of the invention, therefore, to provide an improved process and system for the production of dry, high purity nitrogen product from air.
It is another object of the invention to provide a simplified membrane/deoxo process and system capable of producing dry, high purity nitrogen product.
It is a further object of the invention to provide an improved process and system for the production of high purity nitrogen in essentially dry form, without the significant product loss, contamination of product, and energy consumption associated with the conventional use of an adsorptive (or refrigerative) unit for the removal of moisture from high purity nitrogen product.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.